Refining Search Statements
The next step in developing your search statement is to refine your keyword search string. This may help to narrow or direct your search so that you retrieve the most relevant results. When results are relevant, they are on target or very close to the information being sought. Complex search statements could be refined by adding words and characters such as Boolean operators, quotation marks to indicate exact phrases, truncation symbols, or field search limiters.
Boolean searching is based on a system of symbolic logic developed by George Boole, a 19th century English mathematician. Most computer databases and Internet search engines support Boolean searches. Boolean search techniques help reduce the number of irrelevant documents in the search results.
The power of Boolean searching is based on combinations of keywords with connecting terms called Boolean operators. The three basic operators are the terms AND, OR, and NOT. Many Internet search engines replace Boolean operators with symbols, for example + for AND, - for NOT.
The examples above illustrate general topics expressed with just two keywords. Actual search strings, which express complex topic ideas, may consist of several keywords and combinations of Boolean operators.
The thesis statement "Automobile air bags are not safe for children" might result in the search string:
automobiles AND air bags AND children AND safety
Most databases and major search engines support complex Boolean searches. If you have a complex search using more than one operator, you can nest your search terms, using parentheses. Search terms and operators included in parentheses will be searched first, then terms and operators outside the parentheses. A search for:
(ADD OR attention deficit disorder) AND college students
will search for documents containing either the acronym ADD or the words attention deficit disorder, then narrow the search results only to those documents that also contain the words college students.
These concepts are further illustrated in the Advanced Boolean Searching tutorial by Colorado State University libraries.
Pay attention to phrases in search strings. If you are looking for information on the capital gains tax, you need to enter that part of your search string as a phrase. Otherwise, you may retrieve irrelevant documents which contain all of the keywords, in any order, anywhere in the document. Most search engines and databases support phrase searches. Internet search engines usually require quotation marks to indicate phrases such as: "capital gains tax", "physician assisted suicide", "human genome project".
Another useful search parameter is truncation. Truncation allows the searcher to insert a truncation symbol, usually an * or ?, as a wildcard at the end or the middle of a word. For example, the search term teen* will locate the terms
Try not to use truncation on a very short root word as too many words would be retrieved, and the relevance of the search would be affected. Some search engines automatically truncate your search terms to find plural, -ing, or -ed endings. Truncation symbols will vary. Some search engines and databases do not support truncation.
The concept of truncation is further illustrated in this tutorial by Colorado State University libraries.
Field searching is a technique which allows you to search a particular part of a computer record. For example, in many search engines and electronic databases, you can specify that a specific word in your search string be found in the title of the document. You may also be able to search for an author's last name, a range of dates, full-text documents, or material in a particular language. In web search engines, you may be able to search by domain name, URL, or type of file (picture, sound or video). This search technique works efficiently when you need to narrow your search in a very specific way. Some web search engines make field searching available only in the advanced search mode.